RE: [Sip-implementors] To-Tag value

[Christer Holmberg (KI/LMF)]

Title: Message

Hi,

 

Comments inline ([CHH])

 

Hi,

 

This is related to INVITE transaction on unreliable transport.

 

 UAC                                   UAS

------                                ------

-------------------------------> INVITE

<------------------------------- 300 Multiple choices

--------------------------------> ACK

<------------------------------- 500 Server internal error (before the Timer D fires)

--------------------------------> ACK

 

Suppose the "To-tag" in the second final response (500) sent by UAS is different than the one in the initial response (300),  

 

[CHH] Why would the UAS (I assume it's the same UAS sending both responses) send two different final responses to the INVITE? A UAS only sends one final response to the INVITE (or any request).

 

1. how should the UAC behave? 

 

[CHH] I would accept the 300, send the ACK, and most likely treat the 500 as a retransmit of the 300. 

 

2. And what should be the value of the "To-Tag" in the ACK sent by UAC for 500 response? 

 

[CHH] I would retransmit the ACK I sent for the 300 response, using the same header values.

 

Regards,

 

Christer Holmberg

Ericsson Finland

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